1. Field of the Invention
The present invention relates to a toner for developing an electrostatic charge image in electrographic methods, electrostatic recording methods and electrostatic printings, as well as a developer and an image forming method using the toner.
2. Description of the Related Art
Conventionally, a fine particle external additive with a size of several nm to several ten nm has been used for a toner for developing a latent electrostatic image, and in recent years, large diameter particles typified by large particle diameter silica have been used as additives. A function expected for such large particle diameter silica is to prevent the additive from being embedded in toner base particles to which the large particle diameter silica have adhered, against a load and stress from an outside. Its functionality has been often set forth mainly in terms of particle diameter.
Thus, the present inventors produced a toner using spherical large diameter particles placed in the market, and gave the load from the outside thereto in a test apparatus which mimicked an actual machine. Then, a phenomenon that the spherical large diameter particles tumbled and migrated on the surface of the toner base particles against the load and the stress from the outside was observed from morphological characteristics of the spherical large diameter particles. When an amount of the added spherical large diameter particles was small, its tendency became particularly remarkable. Thus, it was found that a purpose to prevent the additive from being embedded was not always accomplished.
Likewise, from a test using the toner base particles having fine asperities on the toner surface obtained by polymerization for enhancing a cleaning property, it was found that the large diameter particles migrated to concave portions in the asperities due to the load from the outside and did not exert the expected function.
Thus, in order to prevent such a tumbling phenomenon of the external additive on the surface of the toner base particles, a method of giving an effect on a rolling phenomenon by increasing the amount of the external additive to be added to increase a particle number receiving the load from the outside is proposed. According to this method, a certain effect on the outside load is obtained, but the rolling phenomenon of the particles on the surface of the toner base particles is not inhibited and the large particle diameter silica is dissociated from the toner surface to be sometimes free by the stress and friction in a developing device. Such a free external additive migrates together with the toner onto a photoconductor when the toner is developed on the photoconductor surface, remains on the photoconductor surface after the transfer, and sometimes adheres to the photoconductor surface without being cleaned. When the free external additive is accumulated on the photoconductor surface in this way, image quality on copies is sometimes defected (filming) or the photoconductor surface is sometimes injured to cause shortened lifetime of the photoconductor. The free external additive is spilled from the developing device upon development to stain inside a copy machine. Furthermore, the free external additive adheres onto a carrier surface during the development to inhibit giving and receiving the charge between the carrier and the toner, which is one factor which reduces the charge property of the toner.
In order to solve these problems, the method of fixing the large particle diameter silica to the surface of the toner base particles by giving a strong shear upon adding and mixing is proposed (see Japanese patent Application laid-Open (JP-A) No. 2001-066820). However, when the toner base particles having fine asperities on the toner surface obtained by polymerization are used, this propose is not necessarily effective, the large particle diameter silica migrates to concave portions in the asperities due to the strong shear and remains in non-functional sites on the surface of the toner base particles.
Therefore, it is an actual circumstance that it is desired to rapidly provide a toner which prevents the rolling phenomenon of the external additive on the surface of the toner base particles, can prevent the external additive from being embedded due to external stress and combines excellent cleaning ability, image quality and durability even in a small amount to be added, as well as a developer and an image forming method using the toner